MACROMEDIA COLDFUSION 4.5-CFML LANGUAGE Bedienungsanleitung PDF herunterladen (Seite 21)

21Writing CFX Tags with Java

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The returnAsQuery() function, which accepts any Java-style ResultSet object and makes

it available to the calling page as a ColdFusion-style query object. You can cut and paste

this code into other CFX tags that need to return

ResultSet objects as CFML queries.

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The two forms of the getTagAttr() function, which wraps around the attributeExists()

and getAttribute() methods from the CFX API that were used previously in Listing 30.1.

The ﬁrst form requires that the attribute be passed to the tag, and the second form makes

an attribute be considered optional by using a default value when it is not provided. Again,

you can cut and paste these functions into your own CFX tags if you ﬁnd them convenient.

Within

processRequest(), the ﬁrst portion calls getTagAttr() repeatedly to establish the required

and optional attributes for the tag. If any required attributes are missing, an error message will be

shown; optional attributes will be assigned default value when not provided. The next few lines load

the JDBC driver class speciﬁed in the tag’s

driver attribute with Class.forName(), then connect

to the data source by supplying the

connect, username, and password attributes to getConnection(),

then create an object called

dbmd to represent the data source’s metadata structure.

Next, a series of

if and else if tests are used to call the appropriate DatabaseMetaData method

depending on the

action attribute that the tag is being called with. No matter which method ends

up being called (

getTables(), getColumns(), or the like), the result is always a ResultSet object

called

rs. The returnAsQuery() function is then called to return the data in the ResultSet to the

calling ColdFusion page.

The main task of

returnAsQuery() is to create the new CFML query object with the addQuery()

method. That method requires the new query’s column names to be speciﬁed as an array of strings,

so a few lines of code are required ﬁrst to obtain the recordset’s column names using

getMetaData(),

getColumnCount(), and getColumnName() (all described in the Java SDK documentation). Once the

query has been created, it is a relatively simple task to loop through the

ResultSet, adding rows to

the CFML query and ﬁlling it with data from the

ResultSet along the way. See Table 30.6, earlier

in this chapter, for details about the

addQuery(), addRow(), and setData() methods used in this por-

tion of the listing.

NOTE

Please consult the Java SDK documentation for more information on the classes and methods used in this listing (except for the

ones specific to CFX development; those are detailed in the tables at the beginning of this chapter). Most of them are in the

ava.sql package.

Using the New Tag in ColdFusion

To use the new <CFX_DatabaseMetaData> tag in a ColdFusion page, you need to use javac to com-

pile Listing 30.1, then register the resulting DatabaseMetaData.class ﬁle with the ColdFusion

Administrator. These steps are described in the “Getting Started” section earlier in this chapter.

You can then use the tag in any CFML page, such as the simple example shown in Listing 30.4.

This listing creates a page that allows the user to select from the tables in the

ows.mdb database ﬁle

using a drop-down list. When the user selects a table, the names, types, and widths for each of the

table’s columns are displayed (Figure 30.5).

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